To an increasing extent, touch-sensitive panels are being used for providing input data to computers, electronic measurement and test equipment, gaming devices, etc. The panel may be provided with a graphical user interface (GUI) for a user to interact with using e.g. a pointer, stylus or one or more fingers. The GUI may be fixed or dynamic. A fixed GUI may e.g. be in the form of printed matter placed over, under or inside the panel. A dynamic GUI can be provided by a display screen integrated with, or placed underneath, the panel or by an image being projected onto the panel by a projector.
There are numerous known techniques for providing touch sensitivity to the panel, e.g. by using cameras to capture light scattered off the point(s) of touch on the panel, or by incorporating resistive wire grids, capacitive sensors, strain gauges, etc into the panel.
US2004/0252091 discloses an alternative technique which is based on frustrated total internal reflection (FTIR). Light is coupled into a panel to propagate inside the panel by total internal reflection. Arrays of light sensors are located around the perimeter of the panel to detect the light. When an object comes into contact with a surface of the panel, the light will be locally attenuated at the point of touch. The location of the object is determined by triangulation based on the attenuation of the light from each source at the array of light sensors.
US2009/0153519 discloses a panel capable of conducting signals. A tomograph is positioned adjacent the panel with signal flow ports arrayed around the border of the panel at discrete locations. Signals measured at the signal flow ports are tomographically processed to generate a two-dimensional representation of the conductivity on the panel, whereby touching objects on the panel surface can be detected. Tomographic reconstruction, e.g. using the well-known filtered backprojection algorithm, is a processing-intensive operation. Thus, tomographic reconstruction may require significant processing time, especially if a high resolution of the two-dimensional representation is required.